1. Field of the Invention
The present invention relates to solid-state imaging devices, driving methods therefor, and imaging apparatuses, and more particularly, to a solid-state imaging device, a driving method therefor, and an imaging apparatus that can establish a wide dynamic range by acquiring signals of different sensitivities from one pixel and synthesizing the acquired signals.
2. Description of the Related Art
In the field of solid-state imaging devices, e.g., MOS (Metal Oxide Semiconductor) solid-state imaging devices, a technology to achieve a wide dynamic range is known. More specifically, high-sensitivity and low-sensitivity signals are obtained from each pixel by setting different storage times (exposure times), i.e., long and short storage times, to the pixel, and are then synthesized, whereby a wide dynamic range can be achieved. Each pixel includes a photoelectric conversion element, and a plurality of pixels are two-dimensionally arranged in a matrix form in a pixel array section. In addition, in the pixel array section, a vertical signal line is disposed for each column of the arranged pixels.
First Related Art
As one of the related arts of the above-described technology (hereinafter referred to as a “first related art”), a solid-state imaging device having the following configurations is known. Two column circuits (signal processing circuits), each of which is configured to perform predetermined signal processing upon a pixel signal sent through a signal line disposed for a column of pixels in a pixel array section, are disposed for each of a plurality of columns of pixels and perform signal processing in parallel upon high-sensitivity and low-sensitivity signals sent through one signal line from one pixel, respectively (see, for example, Orly Yadid-Pecht and Eric R. Fossum, “Wide Intrascene Dynamic Range CMOS APS Using Dual Sampling”, IEEE TRANSACTIONS ON ELECTRON DEVICES, VOL. 44, NO. 10, pp. 1721-1723, OCTOBER 1997).
The concept of the first related art will be described with reference to FIGS. 1A and 1B. The physical layout of a pixel array section 101 and two column circuit groups 102 and 103 is shown as FIG. 1A. The concept of scanning performed upon the pixel array section 101 is shown as FIG. 1B. The pixel array section 101 has 18 rows×22 columns of pixels for the sake of simplification of the drawing. Each column circuit in the column circuit groups 102 and 103 is disposed for a column of pixels.
A scanning operation performed upon the pixel array section 101 is performed in units of rows of pixels. The process of the scanning operation includes two steps, i.e., an electronic shutter scanning step for eliminating electric charge stored in a photoelectric conversion element included in a pixel and a readout scanning step for reading out electric charge stored in the photoelectric conversion element. In the readout scanning step, two scanning operations are performed.
A period of time corresponding to the period of time taken to scan the area from a row of pixels (hereinafter referred to as a “shutter row”) upon which the electronic shutter scanning is performed to a row of pixels (hereinafter referred to as a “readout row 1”) upon which a first readout scanning is performed, is defined as a storage time 1. A period of time corresponding to the period of time taken to scan the area from the readout row 1 to a row of pixels (hereinafter referred to as a “readout row 2”) upon which a second readout scanning is performed, is defined as a storage time 2. By making the storage times 1 and 2 different from each other, two signals of different sensitivities, i.e., a low-sensitivity signal and a high-sensitivity signal, can be obtained.
Referring to FIGS. 1A and 1B, the storage times 1 and 2 are periods of time taken to scan four rows of pixels and eight rows of pixels, respectively. Therefore, a signal with twice sensitivity can be obtained from each pixel in the readout row 2 compared with a signal obtained from each pixel in the readout row 1. By synthesizing the two signals of different sensitivities obtained from each pixel included in the same row of pixels in a signal processing circuit (not shown) at a subsequent stage, an image signal having a wide dynamic range can be obtained.
Second Related Art
As another related art to achieve a wide dynamic range (hereinafter referred to as a “second related art”), a solid-state imaging device having the following configurations is known. Two electronic shutter scanning operations and two readout scanning operations are performed, and by making time intervals between a first electronic shutter scanning operation and a first readout scanning operation and between a second electronic shutter scanning operation and a second readout scanning operation different from each other, two signals of different sensitivities are obtained. Here, one column circuit is disposed for one column of pixels. The two signals obtained from the two readout scanning operations are processed in the same column circuit (see, for example, M. Mase, S. Kawahito, M. Sasaki, and Yasuo Wakamori, “A 19.5b Dynamic Range CMOS Image Sensor with 12b Column-Parallel Cyclic A/D Converters”, ISSCC Dig. Tech. Papers, pp. 350-351, February 2005).
The concept of the second related art will be described with reference to FIGS. 2A and 2B. The physical layout of a pixel array section 201 and a column circuit group 202 is shown as FIG. 2A. The concept of scanning performed upon the pixel array section 201 is shown as FIG. 2B. The pixel array section 201 has 18 rows×22 columns of pixels for the sake of simplification of the drawing. Each column circuit in the column circuit group 202 is disposed for a corresponding column of pixels.
Two scanning operations are performed upon the pixel array section 201. In a first scanning operation, a period of time corresponding to the period of time taken to scan the area from a shutter row to a readout row is defined as a storage time 1. In a second scanning operation, a period of time corresponding to the period of time taken to scan the area from a shutter row to a readout row is defined as a storage time 2. By making the storage times 1 and 2 different from each other, two signals of different sensitivities, i.e., a low-sensitivity signal and a high-sensitivity signal, can be obtained. Referring to FIGS. 2A and 2B, the storage times 1 and 2 are periods of time taken to scan four rows of pixels and eight rows of pixels, respectively.